Mammalian spermatozoa acquire the ability to fertilize eggs after leaving the testis and during their passage through the epididymis. We have observed that as spermatozoa pass through the organ, their carnitine content increases significantly in cattle, rabbits and hamsters and their cAMP content increases in cattle and rabbits. We have found that there is a close correspondence between the carnitine content of spermatozoa taken from various regions of the rabbit and hamster epididymis and their fertility as reported by other investigators. The research proposed here will investigate the physiological significance of this accumulation of carnitine and cAMP during maturation in the epididymis. We now want to ascertain, both in vivo and in vitro whether spermatozoa retained in certain regions of the rabbit epididymis accumulate carnitine concurrently with acquiring fertility. We will also continue our inquiry into why spermatozoa of many species (man, monkey, cattle, sheep, rodents, rabbit) contain extraordinarily high concentrations of carnitine. The involvement of carnitine in regulating the energy metabolism of spermatozoa, particularly glycolysis, and the oxidation of pyruvate and amino acids will be studied in bovine, sheep and rabbit spermatozoa. We would like also to identify the biochemical mechanisms whereby spermatozoa accumulate carnitine and cAMP. The possibility that acetylcarnitine is accumulated at a faster rate than carnitine will be explored. The transport of carnitine into bovine spermatozoa will be studied in terms of its energy requirements and its specificity towards structural analogs of carnitine. The activity of spermatozoal adenylate cyclase will be studied with special emphasis on its regulatory and physical properties. Finally, we want to determine whether loss of carnitine accompanies the loss of motility that occurs when hamster sperm are diluted.